Earth's song transmitted into space

The European Space Agency’s Cluster mission has confirmed that the high-pitched chirping and whistling caused by Auroral Kilometric Radiation (AKR) radio emissions is beamed into space on a narrow plane, rather than in a diffuse, ever-widening cone shape across the universe.

The sound of these radio waves is therefore much more detectable, should any extra-terrestrials happen to be listening to the aural fingerprint that Earth is transmitting.

The ESA’s Cluster mission – which consists of four nearly identical spacecraft flying in formation – analysed 12,000 separate bursts of AKR and determined that these bursts of radio waves are sent out on a beam-like trajectory.

“We can now determine exactly where the emission is coming from,” says Robert Mutel, University of Iowa, who conducted the three-year study with ESA colleagues. “This result was only possible because of the Cluster mission’s four spacecraft.”

Whenever a burst of AKR washed over each satellite, the scientists were able to triangulate the points of origin and pinpoint them to tiny (galatically speaking) regions in the Earth’s magnetic field, located a few thousand kilometres above where the light of the aurora is formed.

The benefit of this discovery is that AKR is always present with auroras, which have been identified on other planets such as Jupiter and Saturn. Astronomers are now better placed to understand the magnetic environment of those two gas giants, as well as helping in the search for similar planets around other distant stars.

Such a search will require far larger radio telescopes than are currently in existence, but such telescopes are already being designed.

Scientists have known about AKR radiation since the 1970s, which is caused when charged particles from the solar wind collide with Earth's magnetic field, a process that also generates Earth’s famous aurora, the Northern Lights. The radio waves are blocked by the ionosphere, a charged layer over our atmosphere, so they do not reach Earth.

However, the exact nature and behaviour of the AKR transmission has only now been determined by the Cluster mission.

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